Problem: Solve for $n$ : $-29 + n = -9$
Solution: Add $29$ to both sides: $ \begin{eqnarray} \\ -29 + n &=& -9 \\ \\ {+29} && {+29} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{-29 + n} &\hphantom{=}& \hphantom{-9} \\ n &=& -9 {+ 29} \\ \end{eqnarray} $ Simplify. $ n = 20$